What is the first sale doctrine?

One of the exclusive rights granted to the owner of a copyright by the Copyright Act is the right to control distribution of protected works. However, the first sale doctrine says that once a protected work has been sold for a first time, the purchaser can then redistribute the work without the author’s permission. This is why you can resell a book you have purchased without seeking the author’s permission. The first sale doctrine does not apply to sound recordings of music or musical compositions, or to computer programs, however - in those cases, the copyright owner is permitted to prevent their works from being rented (this is why you can rent videos but not CD’s).